Design And Experiment With A Multifunctional Test Bench Composed Of Serial And Parallel Hybrid Solar Energy Collectors For Drying Fruits And Vegetables

Summary Based on China's condition that there is a strong demand of dry fruits and vegetables, this article from the point of view of development and utilization of new energy and reducing energy consumption, designs a solar drying test bench for fruits and vegetables. This test bench collects solar irradiation in order to dry foods in its container. Experiments have been applied on mushroom and hawthorn to prove the solar-collection-effectiveness of this test bench. The result indicates that this test bench is not only cost-effective in operation but also performs well in drying fruits and vegetables. Here is the major research regarding this test bench:(1) General design of a multifunctional test bench composed of serial and parallel hybrid solar drying equipment This test bench uses flat solar heat collection appliance as its major heat collection device to dry fruits and vegetables by draining through Van dry room.The performances of flat solar heat collection appliance and dry room have direct effects on the efficiency and quality of fruit and vegetable drying.(2) Design of heat collection system Heat collection system adopts flat solar collection appliance to connect single solar heat collection panel in series-parallel structure. Through build up of solar connecting pipes, heat is brought into drying system in the form of hot wind.(3) Design of control system Control system utilizes multiple control devices, Frequency conversion governor, Digital display controlling instrument, matchs tuyere and etc to control the temperature and blower rotational speed, meanwhile, it utilizes micro computer timer switch to auto control blower's running time, which reduces human resources and saves energy. Control system also sets up supplementary heating device in order to assist the function when there is weak sunshine or no sunshine.(4) Design of drying system. Drying container for fruits and vegetables adopts the method of van ventilation. The bottom of the container links to air entrance, while the top of the container is installed with air exit,which generate the method of van ventilation; Drying container has fifteen levels, every level installs two sieves which are made by stainless steel, and each diameter is about 10mm. There is no effect on heat streaming when loading materials. Every sieve is designed to 2m2 to facilitate loading.(5) Comparison of drying technologies. Experiment has been applied on drying test bench to test its heat collection effectiveness.Under the conditions of empty load,sunny day,average ambient humidity 36%,temperature 4℃,average solar irradiation 535W/m2,the result indicates temprature difference can reach up to 23.9℃between entry and environment, and up to 18.4℃between exit and environment,and maximum humidity differences of 22.7% and 21.1% between entrance and exit.Under the condition of full load, drying experiment was carried on mushroom and hawthorn,meanwhile nature drying was carried to compare the results.The drying period of mushroom by using solar drying machines was 6 days,which is one time more efficient than 12days by nature drying. And the drying period of hawthorn by using solar drying machines was 10 days, drying period reduced 5 days and by 1/3 with improved quality.